Mechanistic Study of Selective Adsorption of As(V) by a Surface Ion-Imprinted Diatomite-Based Adsorbent

In this study, a novel As(V) ion-imprinted and 4-picolinic acid (4-PA)-grafted porous diatomite (DE)-based adsorbent (As(V)-IID) was prepared by using the surface ion imprinting technique. The results of the selective adsorption experiment show that the adsorption capacity of As(V) on As(V)-IID reaches 62.78 mg/g in a solution with an initial As(V) concentration of 25 mg/L and a pH value that is near pH 4.0 of the imprinting. The selectivity coefficients ( K ) of As(V) with respect to Cr(VI) and Mo(VI) were up to 12.14 and 27.79, respectively. The binding process was described well by the pseudo-second-order kinetics and Weber–Morris and Langmuir models. Fourier transform infrared spectra (FTIR), scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) analyses suggested that the nitrogen of secondary amide and pyridine was the main imprinting site and played a crucial role in the selectivity of binding of As(V) to As(V)-IID. To further validate the sorption mechanisms, density functional theory (DFT) was employed to study the properties of binding of As(V), Cr(VI), and Mo(VI) with As(V)-IID. The computational results showed that the As(V) was selectively recognized by complexing with N-containing functional groups of the As(V)-IID surface into a tridentate mononuclear configuration with a minimal binding energy ( E b ) of −18.16 eV, which was completely consistent with characterization analyses. This work revealed the selective adsorption mechanisms of As(V)-IID for As(V) and provided new insight into the selective recognition of oxyanions from water by ion-imprinted adsorbents.